As is known, many pourable food products, such as fruit juice, UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.
A typical example of this type of package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by folding and sealing laminated strip packaging material.
The packaging material has a multilayer structure substantially comprising a base layer for stiffness and strength, which may comprise a layer of fibrous material, e.g. paper, or mineral-filled polypropylene material; and a number of layers of heat-seal plastic material, e.g. polyethylene film, covering both sides of the base layer.
In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material also comprises a layer of gas- and light-barrier material, e.g. aluminium foil or ethyl vinyl alcohol (EVOH) film, which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material forming the inner face of the package eventually contacting the food product.
Packages of this sort are normally produced on fully automatic packaging machines, on which a continuous tube is formed from the web-fed packaging material; the web of packaging material is sterilized on the packaging machine, e.g. by applying a chemical sterilizing agent such as a hydrogen peroxide solution, which is subsequently removed from the surfaces of the packaging material, e.g. evaporated by heating; and the web of packaging material so sterilized is maintained in a closed, sterile environment, and is folded and sealed longitudinally to form a vertical tube.
The tube is filled with the sterilized or sterile-processed food product, and is sealed and subsequently cut along equally spaced cross sections to form pillow packs, which are folded mechanically to form respective finished, e.g. substantially parallelepiped-shaped, packages.
Alternatively, the packaging material may be cut into blanks, which are formed into packages on forming spindles, and the packages are filled with the food product and sealed. One example of this type of package is the so-called “gable-top” package known by the trade name Tetra Rex (registered trademark).
To open packages of the type described above, various solutions have been proposed, including reclosable opening devices, which substantially comprise a spout, e.g. tubular, defining a through opening and fitted to a surface of the package, about a hole or a removable or pierceable portion in the surface; and a removable, e.g. screw or hinged, cap fitted to a neck portion projecting from the spout on the opposite side to the surface of the package, to outwardly close the spout.
When the opening device is fitted about a hole in the package, the opening of the spout is closed by a membrane made of plastic material, connected integrally to the spout, and detachable from the spout along a preferential, normally circular, tear line. The membrane is normally fixed to the top (i.e. outer) edge of the spout, and is fitted integrally, on the side facing the cap, with a projecting so-called pull ring, which is pulled off by its free end to detach the membrane from the spout along the preferential tear line and so free the opening to pour out the product. More specifically, the pull ring extends inside and at a predetermined distance from the neck portion.
The opening devices are known to be produced, as described for example in Patent EP-B-099992, using a molding unit, which interacts with a web of packaging material to mold a number of opening devices at respective holes in the web or formed in the web upstream from the molding unit.
More specifically, the web is fed through the molding unit, which comprises a first mold on a first side of the web, and two second molds on an opposite second side of the web.
As the web is fed through, the first mold and second molds are movable into a first configuration detached from and therefore not interfering with the first and second side of the web respectively; and, when the first mold and second molds are aligned with each hole in the web, they are moved into a second configuration cooperating with the first and second side of the web respectively.
More specifically, in the second configuration, a projection on the first mold is housed inside the hole, and defines, with a recess on the two second molds, a closed molding cavity, into which the molding material is injected to mold the opening device.
More specifically, the closed cavity comprises a base portion extending parallel to the travelling direction of the web; and a lateral annular portion defined between facing walls of the recess of the projection extending perpendicularly to the travelling direction.
The membrane can therefore be molded inside the cavity, and the pull ring and/or the neck portion of the opening device, to which the cap is fitted, can be molded in the annular portion.
Molding units of the above type cannot be used for molding opening devices, in which the pull ring projects from the membrane inside and a predetermined distance from the neck portion.